#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main() {
    int n = 0;
    scanf("%d", &n);
    int num = 0;
    int ret = 0;
    while (n--)
    {
        scanf("%d", &num);
        ret ^= num;
    }
    printf("%d", ret);
    return 0;
}